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Functional Java is an open source library that supports closures for the Java programming language
There is a newer version: 5.0
package fj;

import fj.data.List;
import static fj.data.List.unfold;
import fj.data.Option;
import static fj.data.Option.none;
import static fj.data.Option.some;
import fj.data.Tree;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * A wrapper for a {@link java.lang.Class} that provides additional methods.
 *
 * @version %build.number%
 */
public final class Class {
  private final java.lang.Class c;

  private Class(final java.lang.Class c) {
    this.c = c;
  }

  /**
   * Returns the inheritance hierarchy of this class.
   *
   * @return The inheritance hierarchy of this class.
   */
  public List> inheritance() {
    return unfold(
            (java.lang.Class c2) -> {
              if (c2 == null)
                return none();
              else {
                final P2, java.lang.Class> p =
                    new P2, java.lang.Class>() {
                      public java.lang.Class _1() {
                        return c2;
                      }

                      @SuppressWarnings({"unchecked"})
                      public java.lang.Class _2() {
                        return c2.getSuperclass();
                      }
                    };
                return some(p);
              }
            }, c).map(c1 -> clas(c1));
  }

  /**
   * Provides this class's type parameter information as a Tree of the type expression.
   * Only descends into Parameterized classes. Non-abstract classes, or classes that don't implement an interface,
   * are treated as raw types. Arrays, Type Variables, and Wildcards are treated as opaque Types.
   *
   * @return The rose tree representing the type expression for this class.
   */
  public Tree classParameters() {
    return typeParameterTree(c);
  }

  /**
   * Provides this class's superclass type parameter information as a Tree of the type expression.
   * Only descends into Parameterized classes. Non-abstract classes, or classes that don't implement an interface,
   * are treated as raw types. Arrays, Type Variables, and Wildcards are treated as opaque Types.
   *
   * @return The Tree representing the type expression for this class's superclass.
   */
  public Tree superclassParameters() {
    return typeParameterTree(c.getGenericSuperclass());
  }

  /**
   * Provides this class's interface type parameter information as a list of trees.
   *
   * @return A list of trees representing the type expressions for this class's interfaces.
   */
  public List> interfaceParameters() {
    List> ts = List.nil();
    for (final Type t : c.getInterfaces()) {
      ts = ts.snoc(typeParameterTree(t));
    }
    return ts;
  }

  /**
   * Provides type parameter information as a Tree of the type expression.
   * Only descends into Parameterized classes. Non-abstract classes, or classes that don't implement an interface,
   * are treated as raw types. Arrays, Type Variables, and Wildcards are treated as opaque Types.
   *
   * @param t The type (class) for which to get the generic type information.
   * @return Type parameter information as a rose tree of the type expression.
   */
  public static Tree typeParameterTree(final Type t) {
    List> typeArgs = List.nil();
    final Tree types;
    if (t instanceof ParameterizedType) {
      final ParameterizedType pt = (ParameterizedType) t;
      for (final Type arg : pt.getActualTypeArguments()) {
        typeArgs = typeArgs.snoc(typeParameterTree(arg));
      }
      types = Tree.node(pt.getRawType(), typeArgs);
    } else {
      types = Tree.node(t, List.>nil());
    }
    return types;
  }

  /**
   * Returns the underlying class.
   *
   * @return The underlying class.
   */
  public java.lang.Class clas() {
    return c;
  }

  /**
   * Constructs a class from the given argument.
   *
   * @param c The argument to construct this class with.
   * @return A class from the given argument.
   */
  public static  Class clas(final java.lang.Class c) {
    return new Class(c);
  }
}